The promise to Kate that Prince William has always kept

As much as we love to write about royal life – like, really love it – we're well aware being an actual royal could be a real pain in the A.

Aside from the million-dollar blowouts, cute outfits and adoring fans, taking up one of the most coveted positions in the world comes with a lot of stuffy protocol.

For the uninitiated, the expectations, rules, and 24/7 surveillance would be suffocating, and perhaps incredibly lonely. If Princess Diana's legacy taught us anything, it's that royal life equals restriction when you look beyond the glitz of the title.

So when Kate Middleton, a verified commoner, was engaged to marry Prince William, heir to the throne, she was right to have her hesitations.

The future Duke and Duchess of Cambridge at their engagement announcement. (Getty)

"Once you married into the Royal Family, you became a Windsor and that was that," Vanity Fair's Katie Nicholl said on the new documentaryKate Middleton: Working Class to Windsor.

"Well, it was different when Kate and William got married.

"When William asked Kate to marry him, he made it very clear that she wouldn’t have to leave her family behind her once she married into his family."

That meant Kate's family, including sister Pippa, brother James and parents Carole and Michael, were welcome to all kinds of royal events.

"He promised her that they’d always stay a part of the family and they have done," Nicholls said. "Whether it’s joining the Queen at Ascot or being on an important barge within the Queen’s fleet at the Diamond Jubilee celebrations, they’ve been there."

The Middletons’ relationship with the Windsors has positively flourished over the years. They've attended Sandringham for Christmas, and Harry and Meghan were even invited to Pippa's wedding to James Matthews.

It must be such a relief for Kate, who now carries such a huge responsibility on her shoulders, to have her family share it with her.

Kate and Will's 2011 wedding. (Getty)

It's pure speculation, but hearing about the shock Diana endured when she entered into royal life may have played a part in Will's decision.

This is a break in tradition we've seen Harry adopt with Meghan, too. The Duchess of Sussex's mother, Doria Ragland, had a significant role in the royal wedding and was front and centre in her daughter's wedding photos.